A local customer edge (CE) host route is generally exchanged between provider edge (PE) devices in a virtual subnet (VS) by means of a routing protocol of a layer 3 virtual private network (L3VPN), so as to implement subnet extension.
A PE device may generate a local CE host route corresponding to an internet protocol (IP) address of a local CE host according to local CE host information recorded in an address resolution protocol (ARP) or neighbor discovery (ND) protocol cache table, and distribute the local CE host route in a virtual subnet based on a routing protocol of an L3VPN, so that other PE devices in the virtual subnet may learn the local CE host route. In addition, the PE device may have a function of ARP or ND protocol proxy. Taking an application scenario of an ARP as an example, when a PE device in a virtual subnet receives from a local CE host an ARP request packet for querying a MAC address of a remote CE host, if the PE device has learned a CE host route corresponding to an IP address of the remote CE host currently, the PE device may serve as a Proxy to return a virtual media access address (VMAC) corresponding to the PE device to a requesting local CE host through an ARP response packet.
Multiple sites exist in a virtual subnet. It is found by practice that, in a case in which multiple PE devices exist in some sites of the virtual subnet to implement multi-home of a site, it is usually easy to form a CE host routing loop. Moreover, after the CE host routing loop is formed, a forwarding path length of a data packet may generally have a relatively large increase, thereby possibly greatly affecting efficiency of data packet transmission between CE hosts.